Camera systems require autofocus (AF) in many applications to ensure that relevant portions of scenes, of varying distances from the camera, are acquired as in-focus image planes. As shown in FIG. 1, focus is achieved at an optimum distance of the sensor from the lens. The goal of an auto-focus system in a camera is to predict this optimum distance based on image information, and utilize on-board mechanics to achieve the optimum distance.
Image sensors have been developed that enable the acquisition of information with reference to the extent of focus of an image using dual pixel autofocus. Certain implementations of dual pixel AF employ phase-detection, wherein a region the size of a standard pixel in an image sensor array is divided into two sub-pixels. By comparing the outputs of the divided sub-pixels, phase-difference autofocus allows an estimation of whether the image is in focus, and provides information to a feedback system to enable rapid convergence to a focused image.
Dividing certain pixels into sub-pixels can lead to imaging artifacts, such as the creation of a defect pixel in the location in which a split-pixel was employed as shown in FIG. 2.